Fifty years ago, on Dec. 14, 1962, reporters gathered for a press briefing at NASA headquarters and heard an unearthly sound: radio signals being beamed back by a spacecraft flying within 22,000 miles of Venus.

The Mariner 2 mission to Venus was the first time any spacecraft had ever gone to another planet.

These days, vivid photographs showing scenes from all around the solar system are so ubiquitous that people might easily forget how mysterious our planetary neighbors used to be.

"The planets were all known to exist by the Mariner 2 mission in 1962, but very little was known about them, and much of what was believed to be true about them turned out to be wrong," says Erik Conway, a historian at NASA's Jet Propulsion Laboratory, which built the Mariner 2 spacecraft.

Scientists back then could only study the planets through telescopes. And Venus, seen through a telescope, was entirely shrouded by opaque clouds. No one knew what might be on the surface.

Radio signals from the Mariner spacecraft were received on three 85-foot antennas like this one, which were built in California's Mojave desert, near Johannesburg in South Africa, and near Woomera in southern Australia.

"Venus was generally believed, especially in the public, to be kind of a warmer Earth," says Conway. "It would be something like a Mesozoic jungle age, maybe even with dinosaurs. "

The Mariner 2 mission was a part of the space race, which started in 1957 with the launch of the Soviet Sputnik satellite. The Soviets were aiming for the moon, but they also were working to send a probe to Venus. So NASA did, too — even though a lot of people thought the idea was crazy. After all, Venus was 36 million miles away, and the trip would take more than three months.

"There was considerable skepticism in places like NASA headquarters itself that you could actually make a spacecraft that would live long enough to get to another planet," Conway says.

On July 22, 1962, a hastily built spacecraft called Mariner 1 was sitting on top of a rocket in Florida. It was equipped with instruments that would let scientists get new information about the temperature, magnetic field and mass of Venus.

But during the launch, the rocket veered off course; safety officers ordered it to self-destruct.

In the California receiver control room, personnel await confirmation that Mariner has begun to scan the planet Venus.

Luckily, the engineers had built a spare probe — Mariner 2. One month later, it took off. This launch also had glitches, but the rocket somehow righted itself, and Mariner 2 was on its way.

This was just the first of a number of miraculous saves. The trip to Venus was hardly smooth. The spacecraft had all kinds of nerve-wracking troubles — things like a solar panel that stopped working and a temperamental Earth-locating sensor. Plus, as the spacecraft moved closer to Venus, temperatures shot up, and engineers worried that the heat would fry it.

"I was continually being called and given a report on things. My nerves had become so taut by this time that I instructed everyone that would call me to start out with one of two sentences: 'There is no problem,' or, 'There is a problem.' I mean, just get it over with," recalled Mariner project manager Jack James in an oral history videotaped by the Smithsonian in 1987. "Quite often, I got calls, 'There is a serious problem.' "

"Indelibly imprinted in my memory is the beautiful sound of the data stream returning from the encounter science experiments during flyby," NASA manager Oran Nicks later wrote in a memoir entitled Far Travelers: The Exploring Machines. "Words could not describe my feelings as the successful return of data from Venus at last provided evidence of a successful mission."

Data from the receivers were teletyped in a coded format to the Jet Propulsion Laboratory in California.

William Pickering, who served as the director of the Jet Propulsion Laboratory during the mission, later said that even he had been struck by the seemingly casual way that they'd communicated back and forth with something so many millions of miles out in space.

"And I must admit that at the time we were passing by the planet Venus, to sit outside and look at the star Venus in the sky and realize that a piece of our equipment was just then going past the planet was really a very surprising thing to do. And one had to, as it were, pull oneself together now and again and realize that this was indeed real, and this was happening," Pickering recalled.

The public loved it. This was the first time that NASA had beat the Soviets in space, after five years of Soviet milestones that included putting the first man in orbit around the Earth. Pickering was invited to be the grand marshal of the 1963 Rose Bowl parade, which featured a float of the Mariner 2 probe.

Mariner 2 showed that the surface of Venus was way too hot for life: more than 700 degrees Fahrenheit. And it set the stage for all the exploration of our solar system that was to come.

By now, every planet in our solar system has been visited in some way, except for the dwarf planet Pluto; NASA's New Horizons probe is headed there and is expected to fly by in 2015.

There, the data was routed to the digital computer at JPL.

"We have really quite a wonderful armada of missions that are currently exploring," says James Green, head of planetary science at NASA headquarters.

The list includes Cassini in orbit around Saturn, Messenger in orbit around Mercury, Curiosity crawling on Mars, and Juno flying toward Jupiter.

Looking forward another 50 years, Green says NASA could conceivably be doing all kinds of new missions, not just flying by or landing. He predicts that samples will be returned from Europa, an ice-covered moon of Jupiter that may have a subsurface liquid ocean, and robotic probes will explore the lakes of Titan, a moon of Saturn that has bodies of liquid ethane and methane on its surface.

"So 50 years, you know, is an enormous leap. All you have to do is sort of look back at the last 50 years, where we've come, and you'll recognize that even what I've just said is probably going to be eclipsed by what we'll really end up doing in that 50-year time frame," says Green.

And we'll keep learning more about the recently discovered planets beyond our solar system, the ones circling other stars.

Printouts of the data were made available to the experimenters.

But some proponents of planetary exploration worry that without adequate funding, NASA won't be able to do big, ambitious missions to other worlds in the future. Planetary science isn't that large a fraction of NASA's budget, and gets only around $1.2 billion out of the space agency's annual total of around $17 billion.

"People are supporting space more than ever, yet the funding, especially for planetary science, is in jeopardy," says Bill Nye, aka "The Science Guy." He's CEO of The Planetary Society, which promotes more space exploration.

The group is worried about proposed cuts of around $300 million to NASA's planetary sciences division. Nye says that money could be used to fund development of another strategic-class mission, meaning a large, capable spacecraft. "And these are the kind of spacecraft that change the world," says Nye.

Meanwhile, good old Mariner 2 is still out there, though it's now a silent piece of space junk. Conway says it is orbiting the sun somewhere between Venus and Mercury. A model of it is hanging in a place of honor at the Smithsonian's National Air and Space Museum.

Transcript

ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

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These days, you can go online or pick up almost any book about our solar system, and you'll see vivid detailed photographs of rocks on Mars or the moons of Saturn. It's easy to forget that not too long ago, the planets were alien and mysterious. That only began to change when NASA launched the first probe to visit another world. NPR's Nell Greenfieldboyce reports that 50 years ago today, a little space probe called Mariner 2 flew past Venus.

NELL GREENFIELDBOYCE, BYLINE: Back in the 1950s, scientists knew that all the other planets existed. They'd been seen through telescopes.

ERIK CONWAY: But very little is known about them, and much of what was believed to be true about them was - turned out to be wrong.

GREENFIELDBOYCE: Erik Conway is a historian at NASA's Jet Propulsion Laboratory, which built Mariner 2. He says, consider Venus, which is entirely covered by clouds.

CONWAY: Venus was generally believed, especially in the public, to be kind of a warmer Earth. It would be something like a Mesozoic jungle age - maybe even with dinosaurs.

GREENFIELDBOYCE: But all that was about to change. In 1957, the Soviets launched the satellite Sputnik, and the space race was on. The Soviets weren't only aiming for the moon. They were trying to send a spacecraft to Venus. So NASA had to do the same, even though a lot of people thought the idea was crazy. Venus was 36 million miles away. Conway says the trip would take over three months.

CONWAY: There was considerable skepticism in places like NASA headquarters itself that you could actually make a spacecraft that would live long enough to get to another planet.

GREENFIELDBOYCE: Nevertheless, on July 22nd, 1962, NASA tried to send a hastily built space probe caller Mariner 1 to Venus. The rocket veered off course. It was ordered to self-destruct. Luckily, the engineers had built a spare probe, Mariner 2. One month later, its launch came close to failing. But the rocket somehow righted itself, and Mariner 2 was on its way. Fifty years ago today, reporters were gathered at NASA headquarters waiting to hear some truly unearthly sounds. On this scratchy recording, laboratory director William Pickering tells them everyone is about to hear live radio signals coming from Mariner 2.

(SOUNDBITE OF ARCHIVED BROADCAST)

WILLIAM PICKERING: So Pasadena can you turn on the signal again, please?

GREENFIELDBOYCE: This was Mariner 2 making its closest approach to Venus, passing within 22,000 miles. Later, Pickering said that even he had been struck by the seemingly casual way that they'd communicated back and forth with something so far out in space.

PICKERING: To sit outside and look at the star Venus in the sky and realize that a piece of our equipment was just then going past the planet was really a very surprising thing to do. And one had to, as it were, pull oneself together now and again and realize that this was indeed real, and this was happening.

GREENFIELDBOYCE: The public loved it. This was the first time NASA had beat the Soviets. It was also a scientific success. Mariner 2 showed that the surface of Venus was way too hot for life. This mission set the stage for all the exploration of our solar system that was to come. Planets are becoming almost familiar places. They've all been visited in some way, except for the dwarf planet Pluto, and NASA's New Horizons probe is headed there now. James Green is director of planetary science at NASA.

JAMES GREEN: We have really quite a wonderful armada of missions that are currently exploring.

GREENFIELDBOYCE: He ticked off a bunch: Cassini is orbiting Saturn, Messenger is at Mercury, Curiosity is on Mars, Juno is flying towards Jupiter. And Green says, 50 years from now, NASA could be doing all kinds of new missions.

GREEN: We're going to be bringing back a sample from Europa.

GREENFIELDBOYCE: That's an ice-covered moon of Jupiter.

GREEN: Or we're going to be wandering around the lakes of Titan.

GREENFIELDBOYCE: That's a moon of Saturn. Its lakes are made of liquid methane.

GREEN: So 50 years, you know, is an enormous leap. And all you have to do is sort of look back at the last 50 years, where we've come, and you'd recognize that even what I've just said is probably going to be eclipsed by what we'll really end up doing in that 50-year timeframe.

GREENFIELDBOYCE: And we'll be learning more about the planets beyond our solar system, the ones circling other stars. Meanwhile, good old Mariner 2 is still orbiting our sun, silently going around somewhere between Venus and Mercury. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.